Voice relaying apparatus and voice relaying method

ABSTRACT

A voice relaying apparatus includes a receiving section for receiving a cell from an asynchronous transfer mode (ATM) network, a plurality of cell assembling/disassembling units for assembling and disassembling the cells, and a transmitting section for transmitting the cells assembled by each of the plurality of cell assembling/disassembling units. 
     Each of the plurality of cell assembling/disassembling units is composed of a cell disassembling section for disassembling the cell received by the receiving section, a detecting section for detecting whether or not the voice relaying apparatus is carrying out a relay switch operation, and a cell assembling section for assembling the cell disassembled by the cell disassembling section and then sending to the transmitting section, if the fact that the voice relaying apparatus is carrying out the relay switch operation is detected by the detecting section.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a voice relaying apparatus and avoice relaying method in order to carry out a digital voicecommunication in an asynchronous transfer mode (ATM).

2. Description of the Related Art

Conventionally, a digital voice communication network for carrying outan inter-office communication in an asynchronous transfer mode is wellknown. In this digital voice communication network, a voice signal isrelayed and twitched in accordance with a procedure described below. Atfirst, a cell received from a relay line is disassembled. As aconsequently, a low-bit-rate coding voice signal is produced. Thislow-bit-rate coding voice signal is further decoded into a PCM voicesignal, of 64 kbps that can be treated within a digital switch and sentto the digital switch. The digital switch switches this PCM voice signaland outputs the switched PCM voice signal. The PCM voice signaloutputted by the digital switch is again encoded into the low-bit-ratecoding voice signal, and then assembled into the cell, and further sentto the relay line.

In the above-mentioned relaying and switching method, each time therelay switch operation is carried out by the digital switch, theprocesses are carried out, such as the disassembling of the cell, thedecoding of the low-bit-rate coding voice signal, the encoding of thePCM voice signal and the assembling of the cell. This results indeterioration of quality of the voice sent and received through thedigital voice communication network and also leads to increase of atransmission delay time of the voice.

As a first conventional technique to solve this problem, JapaneseLaid-Open Patent Disclosure (JP-A-Heisei 9-98169) discloses “VOICERELAYING AND SWITCHING SYSTEM”. In this voice relaying and switchingsystem, a cell received from a relay line is disassembled and convertedinto the low-bit-rate coding voice signal. Then, a predeterminedsynchronous signal is added to this low-bit-rate coding voice signal tothereby generate a pseudo digital voice signal, which is sent to aswitch. If a digital voice signal switched by the switch includes thepredetermined synchronous signal, only the low-bit-rate coding voicesignal is extracted from the digital voice signal, and then assembledinto the cell, and further sent to the relay line.

Accordingly, when a connection destination of the switch is the relayline, the process for decoding the low-bit-rate coding voice signal andthe process for encoding the PCM voice signal can be omitted. As aresult, this case can avoid the deterioration of call quality caused bythese processes and the increase of transmission delay. However, in thisvoice relaying and switching system, because the digital voice signalmust pass through the section for disassembling the cell, the switch andthe section for assembling the cell at a speed of at least 64 kbps, thehardware which operate at high speed is required.

Also, Japanese Laid-Open Patent Disclosure (JP-A-Heisei 10-4415)discloses “DATA TRANSMITTING APPARATUS”, as a second conventionaltechnique. FIG. 1 shows the structure of this data transmittingapparatus. This data transmitting apparatus is provided with a switch(PBX) 704, A transcoder 702 and an ATM multiplexer 701. As the PBX 704,a switch that can function as a relay station is employed. The ATMmultiplexer 701 is composed of a cell assembling/disassembling device(CLAD) 715 for assembling the cell in accordance with data received froma transcoder 703 and a cell assembling/disassembling device (CLAD) 714for assembling the cell in accordance with data received from anotherdata transmitting apparatus and then transmitting to the transcoder 702.

In this data transmitting apparatus, when the PBX 704 does not serve asthe relay station, the transcoder 703 performs a band compression on thedata received from the PBX 704, and sends to the cellassembling/disassembling device 715. Then, the transcoder 702 releasesthe band compression of the signal from the cellassembling/disassembling device 714, and sends to the PBX 704. However,when the PBX 704 serves as the relay station, the transcoder 703 doesnot perform the band compression on the data received from the PBX 704,and sends to the cell assembling/disassembling device 715. Thetranscoder 702 does not release the band compression of the data fromthe cell assembling/disassembling device 714, and sends to the PBX 704.Hence, when the PBX 704 serves as the relay station, the process fordisassembling the cell and the process for assembling the cell can beomitted in the relay station to thereby avoid the deterioration of thecall quality and the increase of the transmission delay caused by theseprocesses, even in a case of a multiple-stage relay.

Moreover, Japanese Laid-Open Patent Disclosure (JP-A-Heisei 9-55753)discloses “METHOD FOR RELAYING AND SWITCHING COMPRESSED VOICE IN ATM”,as a third conventional technique. In this method for relaying andswitching a compressed voice in ATM, it is detected whether or not acell (digital compression voice data) received from an ATM network isrelayed and switched by a digital switch, when it is relayed andswitched by the digital switch and again transmitted to the ATM network.When a cell (digital compression voice data) is received from the ATMnetwork, such a cheek is done that whether or not a relay switchoperation is accomplished by the digital switch. Then, if such a factthat the relay switch operation is accomplished is detected; the cell ispassed without the compression and expansion of the voice data and theassembling and disassembling of the cell.

SUMMARY OF THE INVENTION

Therefore, the present invention has an object to provide a voicerelaying apparatus and a voice relaying method capable of furtherreducing a delay time when a voice signal is switched.

In order to achieve the above-mentioned object, voice relaying apparatusaccording to a first aspect of the present invention includes a celldisassembling section to disassemble the cell received from a networkand a detecting section to detect whether or not the voice relayingapparatus is carrying out a relay switch operation. The voice relayingapparatus assembles the cell disassembled by the cell disassemblingsection if the detecting section detects that the voice relayingapparatus is carrying out the relay switch operation and transmutes theassembled cell to the network.

Also, in order to achieve the above-mentioned similar object, a voicerelaying apparatus according to a second aspect of the present inventioncomprises a receiving section for receiving a cell from an asynchronoustransfer mode (ATM) network, a plurality of cellassembling/disassembling units for disassembling and assembling thecells and a transmitting section for transmitting the cell assembled byeach of the plurality of cell assembling/disassembling units. Each ofthe plurality of cell assembling/disassembling units is composed of acell-disassembling section to disassemble the cell received by thereceiving section, a detecting section to detect whether or not thevoice relaying apparatus is carrying out a relay switch operation, acontroller to select the cell disassembled by the cell disassemblingsection if the detecting section detects that the voice relayingapparatus is carrying out the relay switch operation and a cellassembling section to assemble the cell which is selected by thecontroller, and to supply the assembled cell to the transmittingsection.

Accordingly, if the relay switch operation is being carried out, thelow-bit-rate coding voice signal obtained by disassembling the receivedcell is not decoded into the PCM voice signal. In addition, the signalbefore the pass to the switch is immediately transferred to the relaydestination. As a consequently, it is possible to omit the time whendata is reciprocated between this voice relaying apparatus and theswitch to thereby reduce the delay time when the voice signal isswitched.

Moreover, in order to correspond to an actual ATM network needing thediscrimination between target destinations (relay destinations) if thereare three or more target destination nodes, the voice relaying apparatusaccording to the present invention can further comprise a unit forreporting the relay destination. Furthermore, it can have theconfiguration of transferring the cell to the relay destination bychanging a destination address in accordance with information ofreporting the relay destination.

Moreover, in order to achieve the above-mentioned similar object, avoice relaying method according to a third embodiment of the presentinvention is provided with the steps of disassembling a cell receivedfrom an asynchronous transfer mode (ATM) network, detecting whether ornot a relay switch operation is being carried out, selecting thedisassembled cell if such a fact that the relay switch operation isbeing carried out is detected and assembling the selected cell andtransmitting.

BRIEF DESCRIPTION OF THE DRAWINGS

A more better understanding of the present invention may be achieved byreading a detailed description in conjunction with the accompanyingdrawings, in which:

FIG. 1 is an explanatory diagram for explaining a conventionaltechnique;

FIG. 2 is a schematic block diagram for indicating a configuration of avoice relaying and switching system to which a voice relaying apparatusaccording to an embodiment of the present invention is applied;

FIG. 3 is an explanatory diagram for conceptually showing a positioningof a voice relaying and switching system including the voice relayingapparatus according to the present invention in an ATM network system;

FIG. 4 shows an address table used by multiplexer/demultiplexer toassign a received cell to any one of first to third cell assembling anddisassembling units;

FIG. 5 shows an address table used to generate a destination address inan address indicator when a call is made between a station “A” and astation “B”;

FIG. 6 shows an address table used to generate a destination address inone address indicator when a call is made between the station “A” and astation “C”; and

FIG. 7 shows an address table used to generate a destination addressesin another address indicator when the call is made between the station“A” and the station “C”.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A voice relaying apparatus according to, an embodiment of the presentinvention will be described in, detail below with reference to theattached drawings. FIG. 2 illustratively shows a structure of a voicerelaying and switching system to which the voice relaying apparatusaccording to an embodiment of the present invention is applied. Thisvoice relaying and switching system is provided with a voice relayingunit 1 and a digital switch (hereafter, referred to as “PBX”) 2. Inaddition, FIG. 2 includes a block diagram showing a structure of thevoice relaying unit 1 and a block diagram showing a structure of cellassembling/disassembling units 10, and 30 within this voice relayingunit 1.

At first, FIG. 3 conceptually shows the positioning of the voicerelaying and switching system including the voice relaying apparatusaccording to the present invention in an ATM network system.Communication nodes (stations) “A”, “B” and “C” are installed in thisATM network system. The voice relaying and switching system shown inFIG. 2 is installed each node. Respective virtual channels VC arecreated through the ATM network between the station “A” and the station“B” and between the station “B” and station “C”. Hereafter, thisembodiment is described assuming that this virtual channel VC ispresent. It should be noted that FIG. 2 shows the voice relaying andswitching system installed in the station “B” but the similar voicerelaying and switching systems are also installed in the station “A” andthe station “C”.

The structure of the voice relaying unit 1 according to the embodimentof the present ‘invention will be described below with reference’ toFIG. 2. The voice relaying unit 1 is provided with a first lineinterface section (LINE CARD) 11, a first multiplexing/de-multiplexingsection (MUX/DEMUX) 12, a first cell assembling/disassembling unit(CLAD) 10, a second cell assembling/disassembling unit (CLAD) 20, athird cell assembling/disassembling unit (CLAD) 30, a secondmultiplexing/de-multiplexing section (MUX/DEMUX) 13 and a second lineinterface section (LINE CARD) 14.

The first line interface section 11 is composed of an interface circuitfor connecting this voice relaying unit 1 to the ATM network.

The first multiplexing/de-multiplexing section 12 de-multiplexes a cellreceived from the ATM network into a signaling cell containing signalingdata or a signaling signal and a voice, cell containing voice data or avoice signal, and then sends to any of the first cellassembling/disassembling unit 10, the second, cellassembling/disassembling unit 20 and the third cellassembling/disassembling unit 30. Also, the firstmultiplexing/de-multiplexing section 12 multiplexes the signaling celland the voice cell from any of the first cell assembling/disassemblingunit 10, the second cell assembling/disassembling unit 20 and the thirdcell assembling/disassembling unit 30, and then transmits to the ATMnetwork.

Each of the first cell assembling/disassembling unit 10, the second cellassembling/disassembling unit 20 and the third cellassembling/disassembling unit 30 disassembles the signaling cell and thevoice cell from the first multiplexing/de-multiplexing section 12. Also,each of the first cell assembling/disassembling unit 10, the second cellassembling/disassembling unit 20 and the third cellassembling/disassembling unit 30 assembles internally generated orexternally supplied signals into the signaling cell and the voice cellto be sent to the first multiplexing/de-multiplexing section 12. Thesedetailed descriptions will be discussed in later.

The second multiplexing/de-multiplexing section 13 multiplexes thesignal from any of the first cell assembling/disassembling unit 10, thesecond cell assembling/disassembling unit 20 and the third cellassembling/disassembling unit 30, and then sends to the second lineinterface section 14. Moreover, the second multiplexing/de-multiplexingsection 13 de-multiplexes the multiplexed signal from the second lineinterface section 14, and then sends to any of the first cellassembling/disassembling unit 10, the second cellassembling/disassembling unit 20 and the third cellassembling/disassembling unit 30.

The second line interface section 14 is composed of an interface circuitfor connecting this voice relaying unit 1 to the PBX 2.

Now, the structures of the first cell assembling/disassembling unit 10,the second cell assembling/disassembling unit 20 and the third cellassembling/disassembling unit 30 will be described. It should be notethat since the structures of the second cell assembling/disassemblingunit 20 and the third cell assembling/disassembling unit 30 areidentical to that of the first cell assembling/disassembling unit 30,only the configuration of the first cell assembling/disassembling unit10 will be described. This first cell assembling/disassembling unit isprovided with a cell disassembling section 16, an identification signaladding section 17, a control section 18 and a cell assembling section19.

The cell disassembling section 16 is composed of a first celldisassembling section (CLD) 101 and a second cell disassembling section(CLD) 102. The first cell disassembling section 101 extracts a firstsignaling signal 113 from a signaling cell supplied from the firstmultiplexing/de-multiplexing section 12, and sends the first signalingsignal 113 to the second multiplexing/de-multiplexing section 13. Also,the second cell disassembling section 102 extracts a first voice signal114, which is a low-bit-rate coding voice signal, from a voice cellsupplied from the first multiplexing/de-multiplexing section 12, andsends the first voice signal 114 to the identification signal addingsection 17 and the control section 18.

The identification signal adding section 17 is composed of a decoder(DEC) 103, a signal generator (GEN) 105 and a multiplexer (MUX) 104. Thedecoder 103 decodes the first voice signal 114 from the second celldisassembling section 102 to thereby generate a first PCM voice signal115 of 64 kbps. The generated first PCM voice signal 115 is send to themultiplexer 104. The signal generator 105 generates a synchronous signal116, and sends to the multiplexer 104. This synchronous signal 116 isused as a CLAD identification signal indicative of the first cellassembling/disassembling unit 10. The multiplexer 104 multiplexes thefirst PCM voice signal 115 from the decoder 103 and the synchronoussignal 116 from the signal generator 105, and sends the multiplexedsignal to the second multiplexing/de-multiplexing section 13.

The control section 18 is composed of a coder (COD) 111, a detector(DET) 108, a controller (CNT) 107, a selector (GEL) 110 and an addressindicator (ADR) 106.

The coder 111 converts a second PCM voice signal 118 of 64 kbps from thesecond multiplexing/de-multiplexing section 13, into a low-bit-ratecoding voice signal, and sends it to the selector 110 as a second voicesignal 119. The detector 108 detects a synchronous signal included inthe second PCM voice signal 118, and generates a detection signal 112representative of the detection result. This detection signal 112 issent to the controller 107 and the address indicator 106.

The controller 107 generates a control signal 121 in accordance with adetection signal 120 from the detector 108, and sends the control signal21 to the selector 110. This control signal 121 is such signal that theselector 110 select the second voice signal 119 from the coder 111 ifthe detection signal 120 indicates that the synchronous signal is notdetected, and the selector 110 select the first voice signal 114 fromthe cell disassembling section 102 if the detection signal 120 indicatesthat the synchronous signal is detected. Therefor, the selector 110selects any one of the first voice signal 114 from the second celldisassembling section 102 and the second voice signal 119 from the coder111, in accordance with the control signal 121 from the controller 107,and then sends the selected signal to the cell assembling section 19.The address indicator 106 generates an address indication signal 122 forindicating an address of a transmission destination, in accordance withthe detection signal 120 from the detector 108. This address indicationsignal 122 is sent to the cell assembling section 19.

The cell assembling section 19 is composed of a first cell assemblingsection (CLA) 112 and a second cell assembling section (CLA) 109. Thefirst cell assembling section 112 assembles a second signaling signal117 supplied from the second multiplexer/demultiplexer 13 into asignaling cell. The second cell assembling section 109 assembles thefirst voice signal 114 or the second voice signal 119 sent through theselector 110, into a voice cell. At this time, an address indicated bythe address indication signal 122 from the address indicator 106 is setto the voice cell as a transmission destination address.

Next, the operations of the voice relaying apparatus having theabove-mentioned structure will be described below with reference toFIGS. 2 to 4. Hereafter, a first case in which a call is made betweenthe station “A” and the station “B” and a second case in which the relayswitch operation is carried out in the station “B” to make a callbetween the station “A” and the station “C” are described.

In the first case, if a voice signal is transmitted from the station.“A” to the station “B”, the operation is as follows. At first, when thestation “B” receives a cell sent through the ATM network from thestation “A”, the first line interface section 11 supplies the receivedcell to the first multiplexer/demultiplexer. Then, the firstmultiplexer/demultiplexer 12 de-multiplexes the received cell into asignaling cell and a voice cell. The first multiplexer/demultiplexer 12also assigns the de-multiplexed signaling cell and voice cell to any ofthe first cell assembling/disassembling unit 10 the second cellassembling/disassembling unit 20 and the third cellassembling/disassembling unit 30, in accordance with a destinationaddress noted in the received cell. This assignment is carried out inaccordance with an address table shown in FIG. 4.

For example, if the destination address of the signaling cell from thestation “A” is “bs1”, the received signaling cell is sent to the firstcell disassembling section 101 of the first cellassembling/disassembling unit 10. In this case, since the destinationaddress of the voice cell from the station “A” is “bv1”, the receivedvoice, cell is sent to the second cell disassembling section 102 of thefirst cell assembling/disassembling unit 10.

The first cell disassembling section 101 extracts the first signalingsignal 113 from the received signaling cell, and sends the firstsignaling signal 113 to the second multiplexer/demultiplexer 13. Thesecond cell disassembling section 102 extracts the first voice signal114, which is the low-bit-rate coding voice signal, from the receivedvoice cell, and sends the first voice signal 114 to the decoder 103 andthe selector 110.

The decoder 103 decodes the received first voice signal 114 to therebygenerate the first PCM voice signal 115. Then, the generated first PCMvoice signal 115 is send to the multiplexer 104. On the'other hand, thesignal generator 105 generates the synchronous signal 116 used as theCLAD identification signal.

The multiplexer 104 inserts the synchronous signal 116 from thegenerator 105 into the first PCM voice signal 115 from the decoder 103.In this inserting operation, for example, a particular voice signal isdetermined for each several bytes of the first PCM voice signal 115, andthen the synchronous signal 116 is inserted into LSB (Least SignificantBit) of this particular voice signal. If the synchronous signal 116 isinserted into the first PCM voice signal 115 in this manner, even whenit is decoded into an analog signal by the decoder of the PBX 2, theoriginal voice signal can be reproduced without any actual trouble.

On the other hand, if a voice signal is transmitted from the station “B”to the station “A”, the operation is as follows. Here, let us considerthat a voice signal from the PBX 2 is de-multiplexed by the secondmultiplexer/demultiplexer 13, and is sent to the first cellassembling/disassembling unit 10. In this case, the second signalingsignal 117 from the second multiplexer/demultiplexer 13 is inputted tothe first cell assembling section 112. The first cell assembling section112 assembles this second signaling signal 117 into a cell, and furthersets “as1” indicative of a port 1 of the station “A” as the destinationaddress, and sends to the first multiplexer/demultiplexer 12.

Also, the second PCM voice signal 118 from the secondmultiplexer/demultiplexer 13 is sent to the coder 111 and the detector108. The coder 111 converts this second PCM voice signal 118 into thelow-bit-rate coding voice signal, and sends the low-bit-rate codingvoice signal to the selector 110 as the second voice signal 119.

The detector 108 detects whether or not the synchronous signal iscontained in the second PCM voice signal 118. In this case, the station“B” is under controlling the call between the station “A” and thestation “B”, and is not under controlling the relay, switch operation.Thus, the second PCM voice signal 118 is a signal encoded by a coder(not shown) in the PBX 2. Hence, the second PCM voice signal does notcontain the synchronous signal. As a result, the detector 108 suppliesthe detection signal 120 indicating that the synchronous signal is notdetected to the controller 107 and the address indicator 106.

The controller 107, since the detection signal 120 from the detector 108indicates that the synchronous signal is not detected, selects thesecond voice signal 119 from the coder 111, and then sends the selectedsecond voice signal 119 to the second cell assembling section 109.

Simultaneously with the above-mentioned selecting operation, the addressindicator 106 generates the address indication signal 122 in response tothe detection signal 120 from the detector 108. The address indicationsignal 122 is generated in accordance with, for example, an addresstable shown in FIG. 5. The generate address indication signal 122 issend to the second cell assembling section 109. The second cellassembling section 109 assembles the second voice signal 119 suppliedvia the selector 110, into a voice cell. Then, the second cellassembling section 109 sets the destination address of the voice cell to“av1” indicative of the port 1 of the station “A” in accordance with theaddress ‘indication signal’ 122 from the address indicator 106, and thensupplies to the first multiplexer/demultiplexer 12.

The second multiplexer/demultiplexer 12 multiplexes the signaling cellcontaining the second signaling signal 117 from the first cellassembling/disassembling unit 10 and the voice cell containing thesecond voice signal 119, and sends the multiplexed cells through thefirst line interface section 11 to the ATM network. In the ATM network,the multiplexed cells are transferred to the station “A” in accordancewith the destination address of each cell. In the station “A”, themultiplexed cells are distributed to the port 1, and then decoded intoeach signaling signal and voice signal. These signaling signal and voicesignal are supplied to the PBX. The above-mentioned operations enablethe call to be made between the station “A” and the station “B”.

Next, the second case in which the relay switch operation is carried outin the station “B” to make a call between the station “A” and thestation “C” will be described below. In this second case, since thevirtual channel VC is not present between the station “A” and thestation “C”, the station “A” and the station “C” are connected to eachother through the relay switch operation in the station “B”. A call pathin this second case is composed of a first call path from the station“A” to the station “B” and a second call path from the station “B” tothe station “C”. After the establishment of both the first call path andthe second call path, the PBX 2 in the station “B” connects these twocall paths to each other. This enables the call to be made between thestation “A” and the station “C”. Each of the operation in the first callpath and the operation in the second call path is identical to theabove-mentioned operation (the operation between the station “A” and thestation “B”).

Here, the process carried out in the PBX 2 for connecting the two callpaths is described in detail with reference to FIGS. 2 and 3. For theconvenience of description, let us suppose that the first, cellassembling/disassembling unit 10 in the station “B” is used to connectwith the station “A”, and the second cell assembling/disassembling unit20 in the station “B” is used to connect with the station “C”,respectively.

The PBX 2 sends a signal including the first PCM voice signal 115 towhich the synchronous signal 116 is added, derived from the first cellassembling/disassembling unit 10, namely, the call path from the station“A” to the call path to the station “C”, namely, the second cellassembling/disassembling unit 20. On the contrary, the PBX 2 sends asignal including the first PCM voice signal 215 to which a synchronoussignal 216 is added, derived from the second cellassembling/disassembling unit 20, namely, the call path from the station“C”, to the call path to the station “A”, namely, the first cellassembling/disassembling unit 10. Accordingly, the detector 108 of thefirst cell assembling/disassembling unit 10 detects the synchronoussignal 216 generated in the second cell assembling/disassembling unit20. Also, a detector 208 of the second cell assembling/disassemblingunit 20 detects the synchronous signal 116 generated in the first cellassembling/disassembling unit 10.

Next, the controller 107 generates such a control signal 121 that theselector 110 selects the first voice signal 114 from the second celldisassembling section 102, in accordance with the detection signal 120from the detector 108. The selector 110 selects the voice signal inaccordance with this control signal 121. Similarly, a controller 207generates such a control signal 221 that a selector 210 selects a firstvoice signal 214 from a second cell disassembling section 202, inaccordance with a detection signal 220 from a detector 208. The selector210 selects the voice signal in accordance with this control signal 221.Also, the address indicator 106 generates the address indication signal122, in accordance with the detection signal 120 from the detector 108.Similarly, an address indicator 206 generates an address indicationsignal 222, in accordance with a detection signal 220 from the detector208.

The address indicator 106 generates “av2” as the address indicationsignal 122, in accordance with an address table shown in FIG. 6. Then,the second cell assembling section 109 sends the voice cell in which thedestination address is changed in accordance with the address indicationsignal 122, through the first multiplexer/demultiplexer 12 and the firstline interface section 11 to the ATM network. Accordingly, the voicesignal (the first voice signal 114) from the first cellassembling/disassembling unit 10 is sent to the station “C”.

Similarly, the address indicator 206 generates “av1” as the addressindication signal 222, in accordance with an address table shown in FIG.7. Then, the second cell assembling section 209 sends the voice cell inwhich the destination address is changed in accordance with the addressindication signal 222, through the first multiplexer/demultiplexer 12and the first line interface section 11 to the ATM network. Accordingly,the voice signal (the first voice signal 214) from the second cellassembling/disassembling unit 20 is sent to the station “A”.

The voice signal from this first cell assembling/disassembling unit 10is originally the voice signal from the station “A”, and the voicesignal from the second cell assembling/disassembling unit 20 is thevoice signal from the station “C”. Accordingly, the call path isaccomplished between the station “A” and the station “C”. At this time,the first voice signal 114 and the first voice signal 214, which are thelow-bit-rate coding voice signals, are not decoded into the PCM voicesignals. Moreover, the signal before supplying to the PBX can beimmediately transferred to the relay destination.

The voice, relaying apparatus and the voice relaying method according tothe present invention, when the relay switch operation is carried out inthe ATM network, the low-bit-rate coding voice signal is not decodedinto the PCM voice signal. Moreover, the signal before supplying to thePBX is immediately transferred to the relay destination. Consequently,the time of the reciprocation between the voice relaying apparatus andthe PBX can be shortened and the delay time can be decreased.

1-21. (canceled)
 22. A method comprising: determining, by a device, thata synchronous signal is not detected; selecting, by the device, a voicesignal based on determining that the synchronous signal is not detected;assembling, by the device, a voice cell based on the voice signal; andsending, by the device, the voice cell.
 23. The method of claim 22,where determining that the synchronous signal is not detected comprises:generating a detection signal based on another voice signal, anddetermining that the synchronous signal is not detected based on thedetection signal.
 24. The method of claim 23, where the other voicesignal includes a pulse code modulation (PCM) voice signal.
 25. Themethod of claim 22, further comprising: converting a pulse codemodulation (PCM) voice signal into the voice signal before determiningthat the synchronous signal is not detected.
 26. The method of claim 22,where the voice signal is a low-bit-rate coding voice signal.
 27. Themethod of claim 22, further comprising: generating an address indicationsignal that indicates an address of a transmission destination for thevoice cell; and sending the address indication signal to an assemblingsection of the device that assembles the voice cell.
 28. The method ofclaim 27, where generating the address indication signal includes:generating a detection signal based on determining that the synchronoussignal is not detected, and generating the address indication signal inaccordance with the detection signal.
 29. The method of claim 22, whereselecting the voice signal includes: determining that a relay switchoperation is not being carried out based on the synchronous signal notbeing detected; and selecting the voice signal based on the relay switchoperation not being carried out.
 30. A method comprising: determining,by a device, that a synchronous signal is present in a particularsignal; assembling, by the device, a cell based on a voice signal afterdetermining that the synchronous signal is present in the particularsignal; and transmitting, by the device, the cell.
 31. The method ofclaim 30, where assembling the cell comprises: determining that a relayswitch operation is being carried out based on the synchronous signalbeing present in the particular signal; and assembling the cell based onthe voice signal based on the relay switch operation being carried out.32. The method of claim 30, further comprising: receiving another cellthat is different from the cell; and generating the voice signal basedon information extracted from the other cell.
 33. The method of claim30, further comprising: generating a pulse code modulation (PCM) voicesignal, and generating the voice signal by combining the PCM voicesignal and the synchronous signal.
 34. The method of claim 30, furthercomprising: generating the particular signal based on another voicesignal.
 35. The method of claim 30, further comprising: selecting anaddress based on information included in the synchronous signal afterdetermining that the synchronous signal is present in the particularsignal; and transmitting at least a portion of the particular signalbased on the address.
 36. A system comprising: a network device to:determine whether a synchronous signal is detected based on a detectionsignal; select, when the synchronous signal is detected, a first voicesignal based on the synchronous signal being detected; select, when thesynchronous signal is not detected, a second voice signal based on thesynchronous signal not being detected assemble a voice cell based on thefirst voice signal or the second voice signal; and transmit the voicecell.
 37. The system of claim 36, where, when selecting the second voicesignal, the network device is to: determine that a relay switchoperation is not being carried out based on the synchronous signal notbeing detected, and select the second voice signal based on determiningthat the relay switch operation is not being carried out.
 38. The systemof claim 36, where the network device is further to: generate an addressindication signal; and set an address of a transmission destination forthe voice cell based on the address indication signal.
 39. The system ofclaim 38, where, when generating the address indication signal, thenetwork device is to: generate the detection signal based on determiningthat the synchronous signal is not detected, and generate the addressindication signal in accordance with the detection signal.
 40. Thesystem of claim 38, where the network device is to: convert a pulse codemodulation (PCM) voice signal into the second voice signal beforedetermining whether the synchronous signal is not detected.
 41. Thesystem of claim 36, where the second voice signal is a low-bit-ratecoding voice signal.